The present invention concerns the manufacture of elastic casings as supports used inside tires to bear the weight in case of a flat. More specifically, it concerns the manufacture of supports which have a generally inextensible belt at their base, made by means of reinforcing wires of the type that usually reinforces tires.
Patent Application EP 0,796,747 describes a particular example of such a support. In FIG. 1 of Patent Application EP 0,796,747, it can be seen that the base 10 of the support is reinforced by wires 11 arranged substantially at zero degree relative to a plane perpendicular to the axis of rotation of the support.
In the present invention, xe2x80x9cwirexe2x80x9d is understood to mean monofilaments as well as multifilaments, or assemblages like cords, plies or even any type of equivalent assemblage, whatever the material and treatment of those wires, such as surface treatment or coating or presizing in order to favor adhesion to the rubber. xe2x80x9cZero degreexe2x80x9d is understood to mean an angle measured relative to the circumferential direction, that is, relative to a plane perpendicular to the axis of rotation of the support, thus following the usual conventions for tires. The angle is said to be xe2x80x9csubstantiallyxe2x80x9d zero degree, because the reinforcement making it possible to oppose centrifugation of the support is created by winding of a wire or strip of parallel wires, with a certain pitch, the result being that the angle will not be zero degree in the strict sense, but, in practice, at least locally, slightly greater than zero degree, in order to be able to sweep the entire width desired.
A suitable material for creating such a support is rubber.
Different methods of manufacture of a molded object are known: compression molding, transfer molding and injection molding. Compression molding implies the introduction of the necessary volume of rubber inside the mold before closing it, while transfer molding and injection molding both imply closing of the mold before introduction of the necessary volume of rubber inside. The choice depends, notably, on the quantities planned, injection molding, while more expensive in initial investment, having a lower marginal cost, making possible a more uniform pressure and temperature during the vulcanization reaction and enabling a greater geometric quality to be attained.
But injection and transfer molding lend themselves poorly to producing nonhomogeneous products which are reinforced by flexible reinforcements. In particular, said processes, involving the introduction of material in a closed mold, are ill-suited for use when the reinforcement is a ply of wires, for the wires do not stay in place in the mold, or they stay in place very poorly. The rubber fed into the mold tends to displace the wires when it fills the mold. It therefore poses a major problem to ensure precise positioning of the wires in the vulcanized support. This is why the force feeding of rubber into a closed mold has not been adopted for wire-reinforced rubber parts. It is, for example, well known that tires are not injection molded; first of all, a rough blank is made very close to the final shape of manufacture of the tire, the blank containing the reinforcing wires inserted in the proper places between the different layers of rubber, and the molding is carried out by enclosing the necessary molding elements around the blank.
The object of the invention is to manufacture a support, such as described in patent application EP 0,796,747, by force feeding material into a previously closed mold, while making sure that the position of the reinforcing wires desired by the designer of the support is fully respected.
The invention proposes a method of manufacture of a support intended to be mounted on a vehicle rim, said support having an axis of rotation, a base defined by a substantially cylindrical radially inner face designed to be mounted around said rim, a crown designed to support the weight and a body between said base and said crown, said base having a substantially inextensible circumferential reinforcement, the radially outer face of said crown having a shape departing from the cylindrical shape, the body containing a plurality of axial recesses emerging from said support on at least one side,
said method of manufacture using a mold having an axis corresponding to said axis of rotation, said mold comprising:
an inner core for molding the radially inner face,
a crown molding ring, said ring comprising at least two parts radially separable from each other, said separable parts making it possible to mold said radially outer face of said crown,
at least one shell containing a plurality of axial fingers for laterally molding said body and said recesses, said core, said ring and said shell cooperating to define, at least partially, a closed cavity for molding said support,
said core comprising at least two components and being capable of assuming a molding configuration in which its components form a circumferentially continuous molding surface for molding said radially inner face, the molding surface being defined by a reference diameter "PHgr" corresponding generally to the inner diameter of said support, said core also being capable of assuming a mold stripping configuration different from the molding configuration, defined by an overall length E around said molding surface less than the product of xcfx80 and reference diameter "PHgr", said method of manufacture comprising the following steps:
prefabricating a ring having said circumferential reinforcement;
establishing the mold stripping configuration of said core;
installing said ring on said core;
establishing the molding configuration of said core;
closing the mold and then force feeding into the mold an injectable material which is elastic in final state;
axially separating said shell containing axial fingers, at least partially, in relation to at least one of the components that are the molding ring and the core;
then establishing the mold stripping configuration of said core and radially separating said parts from the crown molding ring;
discharging said support.
In the context of the present invention, a nonpneumatic casing designed to be used alone in normal service will be considered equivalent to a support, an accessory intended to be mounted inside a tire in order to provide it with a means of temporary operation at zero pressure, adjustments of choice of materials and/or of design of the product itself not being the subject of the present patent invention. In other words, this invention is not limited to a specific application of the product. Its use is advantageous whenever molding or mold stripping becomes rather difficult, for example, because the object manufactured is reinforced, notably, by wires. It is not limited to a particular material, provided that the material meets the needs of the support in terms of characteristics in final state and, for the manufacturing phase, provided that the material can be force fed into a closed mold through mold filling ducts.
The invention proposes using pressurized feeding into a closed molding cavity, in combination with an inner core in several parts, whereas single-part cores are generally used when injection or transfer molding is employed because closing of the mold poses no problem, since that occurs prior to filling, and mold stripping of the product generally adapts quite well to stresses on the latter, since it is in a reticulated or vulcanized state, therefore possessing good mechanical properties. Thus, the invention uses, for example, a core in several parts for molding a support whose radially inner face can be directly or easily stripped from the mold, even outside a single-part core, said radially inner face forming a surface presenting, in relation to a strippable surface parallel to the axis of rotation, deviations not exceeding a few millimeters. In general, said core presents a molding configuration and a mold stripping configuration, different in shape from the preceding one, facilitating not only mold stripping, but also facilitating the installation of a ring in the form of an inextensible belt on the core, at the beginning of manufacture of a support.
The invention also extends to a mold adapted for use of the invention by means, for example, of a standard rubber injection machine of the type marketed under the xe2x80x9cREPxe2x80x9d name.
According to the invention, the mold presents an axis corresponding to the axis of rotation of the support to be molded, for molding of a support intended to be mounted on a vehicle rim, said support having an axis of rotation, a base having a generally cylindrical radially inner face intended to be mounted on said rim, a crown intended to bear the weight and a body between said base and said crown, said base comprising a substantially inextensible circumferential reinforcement, said mold having an axis corresponding to said axis of rotation, said mold containing an inner core for molding said radially inner face, said mold containing other parts creating a closed cavity with said core for molding said support, said core consisting of at least two separable molding parts, one of the parts including a molding sector extending circumferentially from a first edge to a second edge and partially defining the molding surface of said radially inner face, said molding sector being extended, directly or indirectly, by an interface extending from said first edge to said second edge and passing the inside of the core, said interface forming one or more bearings generated by a straight line translated parallel to itself and inclined at a first angle relative to the axis of the mold, said molding parts being capable of taking a molding configuration in which said parts form a circumferentially continuous molding surface, defined by a reference diameter "PHgr" generally corresponding to the inner diameter of said support, and a mold stripping configuration through sliding of one part over another part along said interface, said mold stripping configuration having an overall length E less than the product of xcfx80 and the reference diameter "PHgr".
The bearing or all the bearings at the interface or interfaces between rigid parts is or are preferably flat in order to facilitate their machining. Although a core with only two parts, the interface of which is an inclined plane relative to the axis, can be restricted by relative axial sliding, keeping said parts in contact with each other in order to produce a mold stripping configuration which makes it possible to install on top an inextensible ring, it is preferable to use a core containing at least three rigidly separable parts. The core also preferably has a plane of symmetry containing said axis of the mold.